The traditional role of a bishop is to act as head of a diocese or eparchy. Dioceses vary considerably in geographical size and population. A wide variety of dioceses around the Mediterranean Sea which received the Christian faith early are rather compact; whereas those in areas more recently evangelized, as in some parts of Sub-Saharan Africa, South America and the Far East, tend to be much larger and more populous. Within his own diocese a Latin Rite bishop may use pontifical vestments and regalia, but may not do so in another diocese without, at least, the presumed consent of the appropriate ordinary.[5]

A "diocesan bishop" [6] is entrusted with the care of a local Church (diocese).[7] He is responsible for teaching, governing, and sanctifying the faithful of his diocese, sharing these duties with the priests and deacons who serve under him.[8]

To "teach, sanctify and govern"[9] means that he must (1) oversee preaching of the Gospel and Catholic education in all its forms; (2) oversee and provide for the administration of the sacraments; and (3) legislate, administer and act as judge for canon-law matters within his diocese. He serves as the "chief shepherd" (spiritual leader) of the diocese and has responsibility for the pastoral care of all Catholics living within his ecclesiastical and ritual jurisdiction.[10] He is obliged to celebrate Mass every Sunday and Holy Day of Obligation with the intention of praying for those in his care, assign clergy to their posts in various institutions and oversee finances.[11] A bishop is to have a special concern for priests, listening to them, using them as counsellors, ensuring that they are adequately provided for in every way, and defending their rights set forth in the Code of Canon Law.[12] Latin Catholic bishops also must make regular ad limina visits to the Holy See every five years.[13]

Only a bishop possesses the power to confer the sacrament of Holy Orders. In the Latin Rite the minor orders were abolished after the Second Vatican Council. In Eastern Catholic rites, a monastic archimandrite may tonsure and institute his subjects to minor orders; however, the tonsure and minor orders are not considered to be part of the sacrament of Holy Orders.[14]

The sacrament of Confirmation is normally administered by a bishop in the Latin Rite, but a bishop may delegate the administration to a priest. In the case of receiving an adult into full communion with the Catholic Church the presiding priest will administer Confirmation. [15] In the Eastern Catholic Churches, Confirmation (called Chrismation) is normally administered by priests as it is given at the same time as baptism. It is only within the power of the diocesan bishop or eparch to bless churches and altars, although he may delegate another bishop, or even a priest, to perform the ceremony.[16]

On Holy Thursday Latin Catholic bishops preside over the Mass of the Chrism. Though Oil of the Sick for the sacrament of Anointing of the Sick is blessed at this Mass, it may also be blessed by any priest in case of necessity. Only a bishop may consecrate Chrism. In the Eastern Catholic Churches chrism is consecrated solely by heads of Churches sui juris (patriarchs and metropolitans) and diocesan bishops may not do so.

Only a bishop or other ordinary may grant imprimaturs for theological books, certifying that they are free from doctrinal or moral error; this is an expression of the teaching authority, and education responsibility of the bishop.

Prior to the Second Vatican Council, it was also the prerogative of the bishop to consecrate the paten and chalice that would be used during the Mass. One of the changes implemented since the Council, is that a simple blessing is now said and it may be given by any priest.

In both Western and Eastern Catholic Churches, any priest can celebrate the Mass. In order to offer Mass publicly, however, a priest is required to have permission from the local Ordinary - authority for this permission may be given to pastors of parishes for a limited period, but for long-term permission recourse to the diocesan bishop is usually required. A celebret may be issued to travelling priests so that they can demonstrate to pastors and bishops outside of their own diocese that they are in good standing. However, even if a priest does not possess such a document, he may celebrate the sacraments if the local bishop or pastor judges that the visiting priest is a person of good character.[17]

In the East an antimension signed by the bishop is kept on the altar partly as a reminder of whose altar it is and under whose omophorion the priest at a local parish is serving.

For priests to validly celebrate the sacrament of Reconciliation they must have faculties (permission and authority) from the local bishop;[18] however when the penitent is in danger of death, a priest has both the right and obligation to hear the confession no matter where he may be.[19]
To preside at matrimony, Latin Rite priests and deacons must have appropriate jurisdiction or delegation from a competent authority. In the Latin branch of the Catholic Church, the teaching is that it is the couple themselves who administer the graces of the sacrament; thus, although it is normally an ordained person who officiates at a marriage ceremony, a bishop may delegate a lay person to be present for the exchange of vows; this would be done only in extreme cases such as in mission territories. In the Eastern tradition, the clergy not only witness the exchange of vows but must impart a blessing for a valid marriage to have taken place.[20]

Unless a particular bishop has forbidden it, any bishop may preach throughout the Catholic Church [21] and any priest or deacon may also preach anywhere (presuming the permission of local pastor) unless his faculty to preach has been restricted or removed.[22]

The cathedral of a diocese contains a special chair, called a cathedra, sometimes referred to as a throne, set aside in the sanctuary for the exclusive use of its Ordinary; it symbolises his spiritual and ecclesiastical authority.

The pope is the man who possesses the sacrament of Holy Orders as a bishop and who has been chosen to be Bishop of Rome. Because the Catholic Church holds that the "College of Bishops" as a group is the successor of the "College of Apostles", the bishops of the Church in ecumenical council have the authority to govern the Church. However, the Church also holds that uniquely among the apostlesSaint Peter was granted a role of leadership and authority, giving him the right to speak for the Church and making his leadership necessary for the completion of the College. [23] Hence, Catholicism holds that the Bishop of Rome, as successor of Peter, possesses this role: the Pope, uniquely among bishops, may speak for the whole Church, and a council of bishops is incomplete without the approval of the pope. The right to speak on behalf of the Catholic Church does not mean that the pronouncements of any given pope - even in matters of faith and morals - are imbued with papal infallibility; for such a statement to be made it must be subject to the decree of the First Vatican Council, and has been done so only once since that time (Pius XII's declaration of the Assumption of Mary in 1950).

Patriarchs are the bishops who head certain important archdioceses. There are two types of patriarch, those who lead various sui jurisparticular Churches, and those whose epsicopal sees have been granted the ceremonial title of patriarchate. All Eastern Catholic patriarchs fall into the former group, whilst all Latin Catholic patriarchs, except for the Pope, have purely honorary titles.

Major archbishops are the heads of some of the Eastern Catholic Churches. The major archbishops authority within their respective sui juris churches is equal to that of a patriarch, but they receive fewer ceremonial honours.

A cardinal is a member of the clergy appointed by the Pope to serve in the College of Cardinals, the body empowered to elect someone to the papacy; however, on turning 80 a cardinal loses this right of election. Cardinals also serve as papal advisors and hold positions of authority with the structure of the Catholic Church. Under canon law, a man appointed a cardinal must be a bishop (or accept episcopal ordination), or otherwise seek papal permission to decline such ordination. Most cardinals are already bishops when appointed, the majority being archbishops of important archdioceses or patriarchates, the rest already serving as titular bishops in the Roman Curia. Recent popes have appointed a few priests, most of them renowned theologians, to the College of Cardinals and these have been permitted to decline episcopal ordination.

A metropolitan bishop is an archbishop with minor jurisdiction over an ecclesiastical province; in practice this amounts to presiding at meetings and overseeing a diocese which has no bishop.[24] In Eastern Catholicism a metropolitan may also be the head of an autocephalous, sui juris, or autonomous church when the number of adherents of that tradition is small. In the Latin Rite, metropolitans are always archbishops; in many Eastern churches, the title is "metropolitan," with some of these churches using "archbishop" as a separate office.

A titular archbishop or titular bishop is a bishop assigned to a titular see, which is usually the name of a city or town that used to be the seat of a diocese, but whose episcopal see (diocese) is no longer in existence. Titular bishops often serve as auxiliary bishops, as officials in the Roman Curia, in the Patriarchal Curias of Eastern Churches, as apostolic nuncios or apostolic delegates. In recent times, exceptions to this are that a coadjutor bishop uses the title of the see he is assigned to, and a bishop emeritus uses the title of his last residential see.

An auxiliary bishop is a full-time assistant to a diocesan bishop. Auxiliaries are titular bishops without the right of succession, who assist the diocesan bishop in a variety of ways and are usually appointed as vicars general or episcopal vicars of the diocese in which they serve.[26]

A coadjutor bishop is a bishop who is given almost equal authority to that of the diocesan bishop; he has special faculties and the right to succeed the incumbent diocesan bishop.[27] The appointment of coadjutors is seen as a means of providing for continuity of church leadership. Until recent times, there was the possibility of a coadjutor bishop not having the right of succession.

When a diocesan bishop or auxiliary bishop retires, he is given the honorary title of "emeritus", i.e., archbishop emeritus, bishop emeritus, or auxiliary bishop emeritus. An example in usage would be: "Bishop John Jones, Bishop Emeritus of the Diocese of Anytown." For a cardinal, it would be: "Cardinal James Smith, Archbishop Emeritus of the Archdiocese of Anycity."

The appointment of bishops in the Catholic Church is a complicated process with several officials being invoved. In the Latin Church, the local synod, the papal nuncio (or apostolic delegate), various dicasteries of the Roman Curia, and the Pope all take a part; since the 1970s it has become common practice for the nuncio to solicit input from clergy and laity within the vacant diocese. In patriarchal and major archiepiscopal Eastern Churches, the permanent synod, the holy synod, and the patriarch or major archbishop also play a role in the selection of bishops.

The Catholic Church has always taught that bishops are descended from a continuous line of bishops since the days of the apostles, which is known as apostolic succession. Since 1896, when Pope Leo XIII issued the bull Apostolicae Curae, the Catholic Church has not recognised Anglican orders as valid, because of changes in the ordination rites that took place in the 16th century as well as divergence in the understanding of the theology of episcopacy and Eucharist. However, this view has since been complicated because Old Catholic bishops, whose orders are fully recognised as valid by Rome, have acted as co-consecrators in Anglican episcopal consecrations. According to the church historian Timothy Dufort, by 1969, all Church of England bishops had acquired Old Catholic lines of apostolic succession fully recognised by the Holy See.[29]

To remove, then, all shadow of doubt, this holy Council solemnly declares that the Churches of the East, while remembering the necessary unity of the whole Church, have the power to govern themselves according to the disciplines proper to them, since these are better suited to the character of their faithful, and more for the good of their souls.[30]

However, the Holy See does not recognise as valid the orders of any group whose teaching is at variance with core tenets of Christianity (e.g., The Liberal Catholic Church which has a strong theosophist tendency) even though it may use the proper ritual. The recent practice of Independent Catholic groups to ordain women has added a definite cloudiness to the recognition of the validity of orders, as the act of ordaining women as priests or bishops is incompatible with Catholicism and Eastern Orthodoxy. The practice by some Independent clergy of receiving multiple ordinations also demonstrates an understanding of Holy Orders which is at variance with Catholicism and Orthodoxy, both of which hold that a person is either ordained or not.

The everyday dress of Latin Rite bishops generally consists of either a black cassock with amaranth trim and purple fascia or a black suit and clerical shirt along with the pectoral cross and episcopal ring.

A Latin Rite bishop's choir dress, which is worn when attending but not celebrating liturgical functions, consists of the purple cassock with amaranth trim, rochet, purple zuchetto, purple biretta with a tuft, and pectoral cross. On solemn occasions, the cappa magna may also be worn, but its use is rare today except among those Catholics using the Extraordinary Form (the Tridentine Mass).

The mitre, zuchetto, and stole are generally worn by bishops when presiding over liturgical functions. For liturgical functions other than the Mass the bishop typically wears the cope. Within his own diocese, the ordinary also uses the crosier. When celebrating Mass a bishop, like a priest, wears the chasuble. Before the liturgical reforms following the Second Vatican Council, bishops also made use of the pontifical gloves, pontifical sandals, and the pontifical dalmatic; these accoutrements, including the maniple, are rarely seen except within the context of the Tridentine Mass.

The everyday dress of Eastern Catholic bishops is often the same as their Latin-rite counterparts: black clerical suite with pectoral cross or panagia. When attending liturgical functions at which they do not celebrate, Eastern Catholic bishops usually wear a mantya, panagia and a engolpion if he is a patriarch or metropolitan bishop. He will also carry a pastoral staff in the form of a walking stick topped by a pommel. Eastern Catholic bishops do not normally use an episcopal ring.

When participating in the Divine Liturgy, an Eastern Catholic bishop will wear the sakkos (Imperial dalmatic), omophorion, epigonation and Eastern-style mitre. The most typical mitre in the Eastern Catholic churches is based on the closed Imperial crown of the late Byzantine Empire. It is made in the shape of a bulbous crown, completely enclosed, and the material is of brocade, damask or cloth of gold. It may be embroidered, and richly decorated with jewels. There are normally four icons attached to the mitre: (Christ, the Theotokos, John the Baptist and the Cross. Eastern mitres are usually gold, but other liturgical colours may be used. The mitre is often topped by a cross, either made out of metal and standing upright, or embroidered in cloth and lying flat on the top. He will also carry a crosier of the Eastern style.